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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

464

GLYCERINE

the purity, and various quantitative determinations to decide its commercial
value or its fitness for definite purposes.

A.   Crude Glycerine

Glycerine liquors from soap-works, either as they are or after concen-
tration (as usually sold) are highly contaminated with various mineral
salts (chlorides, sulphates, sulphides, sulphites, thiosulphates, lime, alkali)
and organic substances (soaps, tarry substances, proteins, etc.). Their
analysis is usually restricted to determinations of the alkali (free and com-
bined), free acid, residue on evaporation, water and glycerine.1

Sampling.:—The sample should contain portions from every vessel
forming the parcel and should be taken, if possible, as soon as these are,
filled, since crude glycerine often contains suspended matters which are
gradually deposited.

If such deposition has already occurred, a good average sample may
be obtained with the help of a special sampler.2

Note is made of any suspended matter observed while the sample is
being taken, and also of the temperature and of the form and capacity of
the vessels when these are not similar.

1.  Ash and Total Alkali.—From 2 to 5 grams of the glycerine are
weighed in a platinum dish and evaporated carefully over a direct flame
and the residue charred at the lowest possible temperature.

The carbonaceous mass is then extracted with boiling water, filtered
and washed. The filter and the contained charred mass are incinerated
in the same dish, the aqueous extract and wash-waters being added and
the whole evaporated to dryness on a water-bath and again ignited, carefully
so that the ash does not fuse.

The ash thus obtained is weighed and then dissolved in water and titrated
with normal acid (indicator : methyl orange), the alkalinity being expressed
as percentage of Na20 in the glycerine.

2.  Free Caustic Alkali.-—20 grams of the glycerine are weighed in
a 100 c.c. flask, dissolved in 50 c.c. of recently boiled water, treated with
excess of barium chloride solution and I c.c. of alcoholic phenolphthalein
solution, made up to volume with boiled water, shaken vigorously and left
at rest.    Subsequently 50 c.c. of the clear liquid are pipetted off and titrated
with normal acid.    The free alkali is calculated as Na20 per 100 parts of
glycerine.

3.  Alkali as Carbonate.—10 grams of the sample are diluted with
50 c.c. of distilled water, treated with sufficient normal acid to neutralise
the total alkali (see i) and boiled, in a reflux apparatus for 15-20 minutes.
The condenser is washed down with recently boiled distilled water and the
free acid titrated with normal soda in presence of phenolphthalein.

The result is calculated as percentage of Na20 and from this is deducted

1 The methods were fixed in 19:1 by an International Commission of American,
English, German and French analysts, as a result of the Congress of Glycerine manu-
facturers held in London in 1909.

3 Described in Zeitschr. angew. chem., 1911, I, p.86$,andL'Industriachimica, 1911,
P- 245. surface of the foot-note.mately N/40 solution) and the titer,